Update yuki.html

Changes:
1. Header image: A 24px portrait image is added to header inline.
2. Nicer fonts: Google font 'Source Sans Pro' is used with different font-weights for headings and text.
3. {CustomCSS} is added  
4. Photo: Caption is displayed in second column under date
5. Photoset: A small (250px) photoset is displayed in second column under date
6. Quote: The image in source is styled like a avatar (round corner, 64px x 64px)

Implemented in http://soumyabg.tumblr.com